In the past, there has been developed a technique of selecting a welding line by displaying on a display screen three-dimensional CAD data input to a computer and allowing an operator to assign a welding line, where welding is to be performed, using graphic data of a workpiece. Such a welding-line selecting method is employed in an offline teaching system that prepares an operating path of a welding robot and teaches the desired operation to the robot.
With the welding-line selecting method described above, however, as illustrated in FIG. 10, a workpiece figure displayed on a display screen may include multiple welding lines and unrelated lines, and the curved parts are approximated by many short straight lines. Therefore, there is a problem in that accurately selecting only necessary welding lines from the multiple lines while looking at the workpiece figure displayed on the display screen is troublesome, and wrong lines may be selected.
To solve such a problem, PTL 1, PTL 2, etc. disclose methods for extracting edge lines at the contacting parts of members as a welding line. PTL 3, PTL 4, etc. disclose methods of extracting a welding line from contact parts in a virtual assembly and welding line candidates by assigned the welding line candidates in advance in a three-dimensional system.